Normally, an occupant protection device is mounted in a vehicle in order to protect the occupant from impact shock. Examples of the occupant protection device include an airbag device and a seat belt pretensioner.
An airbag device rapidly inflates a bag by the combustion gas of the gas generating agent when the vehicle crashes at high speed, to prevent the occupant from strongly hit against a hard part inside the vehicle such as a steering wheel, front window shield, and the like. When a vehicle crash occurs at high speed, the seat belt pretensioner instantaneously draws in the seat belt using the combustion gas of a gas generating agent, to prevent the occupant from being thrown out frontward.
The performances required for the gas generating agent for use in occupant protection device include a gasification rate of 70% or greater and a combustion speed of 8.0 mm/seconds or greater (under the nitrogen gas atmosphere pressurized to 7 MPa). High rate of gasification contributes to the reduction of the amount of gas generating agent to be charged into the gas generating device, and downsizing and weight reduction of the occupant protection device. More preferable rate of gasification is 75% or greater.
As a gas generating agent for use in airbag devices and seat belt pretensioners, non-azide gas generating agents containing no sodium azide have been developed. A main component of conventional non-azide gas generating agents is nitrocellulose. Nitrocellulose is preferable in terms of enhancement of the rate of gasification. However, nitrocellulose has a disadvantage that it generates large amount of carbon monoxide when it is combusted, and that it tends to deteriorate at high temperature (low heat resistance).
In recent years, there is a need for a non-azide gas generating agent which satisfies not also the requirements of the gasification rate and the combustion speed, but also the nature which substantially generates no carbon monoxide (carbon monoxide requirement or combustion gas requirement) and the requirement of high heat resistance.
A conventional non-azide gas generating agent for occupant protection device contains an oxidizing agent. Examples of the anti-oxidizing agent include chlorates, perchlorates, nitrates, and nitrites of ammonium, alkali metals and alkali earth metals, which are capable of achieving high gasification rate.
Patent document 1 discloses a non-azide gas generating agent containing ammonium perchlorate as an oxidizing agent and starch as a fuel. Patent document 2 discloses a non-azide gas generating agent containing ammonium nitrate as an oxidizing agent and polyacrylamide as a fuel. Patent document 3 discloses a non-azide gas generating agent containing ammonium nitrate as an oxidizing agent and 5-aminotetrazole as a fuel. These non-azide gas generating agents satisfy the requirement of high gasification rate, the requirement of high heat resistance, and the requirement of combustion gas.
Patent document 1: Japanese Laid-Open Patent Publication No. 2001-2488
Patent document 2: Japanese Laid-Open Patent Publication No. 2000-103691
Patent document 3: Japanese Laid-Open Patent Publication No. 10-130086
A conventional gas generating agent usable in the vehicle occupant protection device has predetermined oxygen balance and the kind of the oxidizing agent, in order to generate combustion gas containing no carbon monoxide and to maintain the gasification rate to be high. However, the ignitability and combustibility of the non-azide gas generating agent decreases as its gasification rate increases. For this reason, although the conventional gas generating agent usable in the vehicle occupant protection device has high gasification rate, its ignitability is very poor and its combustibility is low.